The present invention relates to a brake system used for a heavy-duty truck or bus, and more particularly, to a brake adapted to supplement the capacity of a main brake system for obtaining sufficient braking in a heavy duty vehicle.
Heavy duty trucks, buses or the like, being heavy in weight and load need good braking capacity for sufficient braking performance. However, there is a problem in that a main brake system alone cannot hold the heavy weight, load and vehicle itself due to oversized parts and load concentrations, such that an appropriate supplementary brake is provided in the form of an exhaust brake, retarder and the like.
Among such supplementary brakes, the exhaust brake is typically mounted inside the exhaust pipe including a butterfly valve by which exhaust gas discharged from the engine is blocked to reduce engine revolutions and thereby slow down the speed of the vehicle when braking power is needed. However, in such a brake, if back pressure inside the exhaust pipe rises beyond a critical level, erroneous operation occurs in the engine exhaust valve, causing damage to the engine. Also, because the butterfly valve cannot be completely closed, it is difficult for an exhaust brake to obtain a sufficient braking performance as a supplementary brake.
Furthermore, there is a problem with the butterfly valves typically employed in that the back pressure of the exhaust pipe generated when the exhaust brake is operated gradually deteriorates the exhaust brake capability.
The present invention provides a supplementary brake for a vehicle adapted to be used particularly in diesel-engine, heavy-duty commercial vehicles as an improved exhaust brake for improved braking capability and durability.
In accordance with an embodiment of the present invention, there is provided an oil pressure supplying means and oil pressure control means for controlling the oil pressure supplied from the oil pressure supplying means. A pulsatory pressure forming means forms a pulsatory pressure in the oil pressure supplied from the oil pressure control means in accordance with the profile of an engine injection cam. A valve opening and closing means opens and closes the exhaust valve of the engine according to pulsatory pressure formed by the pulsatory pressure forming means. A controller controls the oil pressure supply means according to the operating state of the engine.